In October 2010, I am moving to an independent faculty position at Northwestern University to pursue the functional analysis of Kaposi's saroma-associated herpesvirus (KSHV) microRNAs (miRNAs). MiRNAs are -22 nucleotide long non-coding RNAs that posttranscriptionally repress mRNAs bearing imperfect matches to the miRNA, primarily in their 3'UTR. KSHV expresses a number of viral miRNAs from 12 pre-miRNAstem loops during latent infection. During the K99 phase ofthis award, I have comprehensively identified targets of all KSHV miRNAs using the newly developed PAR-CLIP technology and characterized the role of KSHV mJR-KI in the evasion of p53-mediated cell cycle arrest by KSHV. My research goal for the ROO phase of this award is to use this detailed knowledge ofthe KSHVmiRNAtargets to study the contribution ofthe KSHV miRNAs to the de-regulation of cell cycle progression and apoptosis by KSHV. Interference with these pathways by KSHV is thought to be critical for the tumorigenic properties of this virus. The interplay of the KSHV miRNAs with these pathways will be studied (a) based on PAR-CLIP-identified targets of these miRNAs with known functions in cell cycle regulation and the induction of apoptosis, (b) through systematic functional interrogation of B-cell lines or endothelial cells which ectopically express individual or multiple KSHV miRNAs, and (c) through systematic functional interrogation of latently KSHV infected primary effusion lymphoma (PEL) cells or endothelial cells in which the function of individual or multiple miRNAs has been blocked using sponges. I will monitor my development as an independent researcher through regular meetings with a newly formed mentorship committee of experts in herpesvirology miRNA biology. Furthermore, I expect that the proposed research will yield sufficient interesting data to apply for an ROI grant early in the independent phase and also significantly shape my long term research program.